Chemicals that we use every day in homes, industry,
and agricultureincluding detergents, disinfectants, fragrances,
fire retardants, nonprescription drugs, and pesticides (fig. 1)can enter Colorado's streams and ground water with wastewater.
These wastewater chemicals can be released to the environment through
discharges from industrial facilities, animal feed lots, wastewater
treatment plants (WWTPs), individual septic disposal systems (ISDSs),
or through runoff from land applications in agricultural and urban
areas.

Figure 1. Chemicals that we
use every day in homes, industry, and agriculture can enter
Colorado's streams and ground water with wastewater.

The human health and environmental effects of wastewater
chemicals are not well understood, and standards to protect human
health or aquatic life have not been established for most of these
chemicals. Some chemicals, however, such as the detergent degradation
product nonylphenol and the fragrances AHTN and HHCB, have been
shown to disrupt reproduction and growth in fish by affecting endocrine
systems (Thorpe and others, 2001; Schreurs and others, 2004). Other
chemicals, such as the antimicrobial disinfectant triclosan found
in many liquid soaps, dishwasher powders, and plastics, are suspected
of increasing the antibiotic resistance of bacteria in the environment
(McMurry and others, 1998) or of reducing algae diversity in streams
(Wilson and others, 2003). Little is known about the effects of
many other individual chemicals or about the potential additive
or interactive effects of mixtures of these chemicals.

Until recently, there have been few analytical methods
capable of detecting these chemicals at the low concentrations found
in the environment (Kolpin and others, 2002). The U.S. Geological
Survey (USGS) National Water-Quality Laboratory in Denver, Colo.,
has developed a new analytical method to measure concentrations
of 62 wastewater chemicals in water (Zaugg and others, 2002). Methods
were developed to measure these particular chemicals because they
are expected to enter the environment through common wastewater
pathways, are used in significant quantities, may have human or
environmental health implications, and can be accurately measured
in environmental samples by using available technologies (Kolpin
and others, 2002).

What do we know about the occurrence
of these chemicals in Colorado?

The USGS, through its National Water-Quality Assessment
and Toxic Substances Hydrology programs and in cooperation with
local agencies, has conducted a small number of studies of the occurrence
of wastewater chemicals in streams and ground water in Colorado
(fig. 2). This report describes results from four types of sites
— streams in urban areas, streams in forested areas, ground
water from domestic wells, and ground water from municipal wells —
sampled between August 2001 and September 2003. Results
for individual chemicals are grouped into 12 major general-use
categories, such as fragrances and disinfectants (fig. 3), as has
been done previously (Kolpin and others, 2002). For chemicals
having multiple uses or sources, a primary use of the chemical was
chosen for categorization purposes. Because sampling was done during
separate studies, different numbers of samples were collected at
each type of site. Differences in the number of chemicals detected
among site types may be due to differences in the number of samples
collected, as well as to differences between site-type characteristics.
The total number of samples and the frequency of detection (in percent)
are shown along the top of each plot to allow easier comparison
between site types. All data shown in figure 3 are available at
http://waterdata.usgs.gov/co/nwis/qw/.

Figure 2. The U.S.
Geological Survey has conducted a small number of studies in
Colorado examining the occurrence of wastewater chemicals in
streams in urban and forested areas and in ground water from
domestic and municipal wells.

Between August 2001 and September 2003, 23 samples
were collected at 15 sites on urban streams: 10 were in the
South Platte River basin, 4 were in the Arkansas River basin, and
1 was in the Upper Colorado River basin. The areas draining to these
sites ranged from moderately to highly urbanized. Some sites were
located immediately downstream from a single large WWTP discharge
site, whereas others were located farther downstream from one or
more WWTP discharge sites of various sizes. All may have been affected
at some point in their upstream drainage area by ISDS leachate or
agriculture.

Between October 2002 and September 2003, 17 samples were collected
at 1 forested stream site. The site was located on the Cache
la Poudre River, upstream from its confluence with the North Fork
of the Cache la Poudre River. Most of the drainage area upstream
from the site is in either the Roosevelt-Arapahoe National Forest
or Rocky Mountain National Park. The river is used for fishing,
whitewater rafting, and kayaking, and there are campgrounds and
isolated private homes with ISDSs along the river. There is very
little urban development and no WWTP discharge site upstream from
the study site.

Figure 3. A new analytical method
developed by the U.S. Geological Survey measures concentrations
of 62 wastewater chemicals in water. Measurable concentrations
of one or more of these wastewater chemicals were found in streams
in urban and forested areas and in domestic and municipal wells.

One sample was collected from each of 75 domestic wells between
September 2001 and August 2003 (Brendle, 2004; Ortiz, 2004a
and b). The wells were completed in the fractured-rock and sedimentary
aquifers in Park County, Colo., about 30 miles southwest of Denver.
Increasing development in Park County has led to an increase in
the number of ISDSs in the region. Depending on the permeability
of the aquifer, the distance from the ISDS to the well, and the
rate of water flow in fractures, ISDS effluent potentially can reach
shallow ground water before concentrations of contaminants are reduced
substantially.

One sample was collected from each of 12 municipal wells in Arapahoe,
Douglas, and Elbert Counties, Colo., between March and October 2003.
The wells were completed in the Dawson aquifer, the uppermost aquifer
of the Denver Basin aquifer system. The northern part of the Dawson
aquifer is located in the southern metropolitan area of Denver,
and along with the three underlying aquifers of the Denver Basin,
it is used primarily for drinking water and lawn irrigation (Robson,
1987). In the southern metropolitan area of Denver, where ground
water is an important source of drinking water, urban development
could make the water supply in the Dawson aquifer more vulnerable
to contamination.

The few data currently (2004) available indicate that urban streams
were the most vulnerable to contamination, with one or more wastewater
chemicals being found in 100 percent of samples from urban streams,
and with 57 of the 62 wastewater chemicals being detected in
at least 1 sample from these sites. Concentrations also tended to
be highest in urban streams compared to the other site types, with
total concentrations above 1 microgram per liter (µg/L or
part per billion) occurring in 8 of the 12 general-use categories
(antioxidants, detergent metabolites, disinfectants, fire retardants,
fragrances/flavors, nonprescription drugs, PAHs, and steroids) and
total concentrations above 10 µg/L occurring in 3 of the 12
general-use categories (detergent metabolites, fire retardants,
and nonprescription drugs).

Samples from the domestic wells generally had a lower number of
wastewater chemicals detected and at lower concentrations compared
to the urban streams sampled. However, a wide variety of chemicals
also were detected (34 of 62) in the domestic wells. Total concentrations
above 1 µg/L occurred in 7 of the 12 general-use categories
(detergent metabolites, disinfectants, fire retardants, fragrances/flavors,
plasticizers, solvents, and steroids).

The forested stream had fewer wastewater chemicals detected (11
of 62) and at lower concentrations compared to the urban streams
and domestic wells sampled. Total concentrations above 1 µg/L
occurred in only one general-use category (detergent metabolites).

The municipal wells sampled had the fewest wastewater chemicals
detected (6 of 62) and the lowest concentrations measured of the
four site types. Total concentrations were below 1 µg/L in
all general-use categories.

No concentrations of individual chemicals exceeded currently (2004)
established drinking-water standards in any of the samples; however,
no standards have been established for most of these chemicals (U.S.
Environmental Protection Agency, 2004). Concentrations of caffeine,
DEET, nonylphenol, and triclosan, four of the more commonly detected
chemicals at each site type, are shown in figure 4. The U.S. Environmental
Protection Agency is developing aquatic-life criteria for nonylphenol
because of its potential for endocrine disruption (U.S. Environmental
Protection Agency, 2003), and triclosan is of concern because
it may increase the antibiotic resistance of bacteria in the environment.
Both chemicals were frequently detected in urban stream samples;
triclosan also was present in samples from domestic and municipal
wells.

Figure 4. Caffeine, DEET, nonylphenol,
and triclosan were four of the more commonly detected chemicals
at each site type. The U.S. Environmental Protection Agency
is developing aquatic-life criteria for nonylphenol because
of its potential for endocrine disruption, and triclosan is
of concern because it may increase the antibiotic resistance
of bacteria in the environment.

Wastewater chemicals were detected more frequently and generally
at higher concentrations in samples from urban streams and domestic
wells than in samples from the forested stream and municipal wells.
The results indicate hat urban streams and domestic wells in Colorado
may be vulnerable to contamination by wastewater chemicals. However,
the detection of low concentrations of wastewater chemicals in the
forested stream and deeper municipal wells indicates that these
chemicals can be found in streams or ground water even in areas
where there are no obvious sources of waste contamination nearby.

Where do we go from here?

Although data are available from only a limited number
of sites in Colorado at this time, these results indicate that mixtures
of wastewater chemicals are present at low concentrations at numerous,
and sometimes unexpected, locations in the State. Other USGS studies
have found hormones, antibiotics, and prescription drugs in urban
streams receiving WWTP effluent across the Nation, including parts
of the South Platte River (Kolpin and others, 2002; Barnes and others,
2002). The laboratory methods for measuring hormones, antibiotics,
and prescription drugs in water are being developed and are nearing
approval for general use by the USGS. Laboratory methods for the
detection of wastewater chemicals in biosolidssolid or semi-solid
residue generated during the treatment of domestic sewage and recycled
as surface-applied fertilizeralso are being developed by the
USGS.

For more than 100 years, the USGS has been successfully
partnering with State and local agencies to fund water-resources
studies through the Cooperative Water Program. These initial findings
on wastewater chemicals in Colorado's streams and ground water,
along with the new analytical methods being developed by the USGS,
provide a starting point for further investigation into the occurrence,
fate, and environmental effects of wastewater chemicals in Colorado
and across the Nation.